1. Field of the Invention
The present invention relates to an engine-output control unit provided with an electronic-control throttle system for electronically controlling the opening degree of a throttle valve for adjusting the air quantity to be taken into an engine in accordance with operational information including engine speed and gear information.
2. Description of the Prior Art
A conventional vehicle controls the output of an engine by mechanically operating a throttle valve set in the intake pipe of the engine in accordance with the accelerator control input of a driver and thereby, adjusting the intake air quantity of the engine.
Because recent engines are computerized, an electronic-control throttle system such as one disclosed in the Japanese Patent Laid-open No. 201061/1990 is noticed which electronically operates a throttle valve by electrically detecting an accelerator control input (opening degree of accelerator). The electronic-control throttle system computes the target torque of an engine in accordance with an accelerator opening degree, vehicle speed, and engine speed, operates the throttle valve with an electric motor, and controls the output of the engine.
Because this type of the electronic-control throttle system can accurately control an intake air quantity for determining the combustion state of an engine, it is used, for example, for advanced engine combustion control for clearing various gas regulations becoming stricter year by year. That is, by controlling the air quantity to be taken into an engine by the electronic-control throttle system in addition to conventional control of fuel quantity to be supplied to an engine, it is possible to accurately control an air-fuel ratio (ratio of air quantity to be taken into an engine to fuel quantity to be supplied to the engine) greatly influencing the characteristics of the gas exhausted from the engine. Therefore, it is possible to realize a combustion state corresponding to a driving state, reduce the amount of exhaust gas, and control an engine output corresponding to a vehicle running state or driver's manipulation. Thus, it is possible to optionally set output control corresponding to an engine-side request and obtain highly flexible engine-characteristics.
Moreover, in the case of an engine for performing very rarefied combustion such as a cylinder-injection-of-fuel engine which is recently noticed as an art capable of meeting the needs such as reduction of fuel consumption, reduction of exhaust gas, and improvement of engine output which are apparently reciprocal, it is necessary to precisely control the intake air quantity of an engine in order to decrease the fluctuation of engine output torque when normal combustion and rarefied combustion are changed under a driving state in which the opening degree of an accelerator is constant, that is, under a state in which the torque requested for the engine by a driver is constant. In the case of the cylinder-injection-of-fuel engine, because the rarefactive degree of fuel is high compared to that of a conventional rarefied-combustion engine, the control range of the intake air quantity is wide and therefor, it is necessary to further precisely control the intake air quantity.
As a unit for controlling the intake air quantity of an engine, there is a unit for controlling the idling speed of the engine by closing a throttle valve under the idling state of the engine and controlling the air quantity of an air duct bypassing the throttle valve in an intake pipe with an air control valve. Moreover, as units for controlling the output of an engine by controlling a throttle valve only for a specific driving state, there are a cruise-control unit for feedback-controlling a vehicle to a vehicle speed set by the driver and a traction control unit for reducing the output of an engine when a tire slips on a slippery road surface at the start of the vehicle.
The above-mentioned electronic-control throttle system simultaneously controls these engine outputs and thus, realizes simplification of the system structure of the entire engine and advanced control.
When a vehicle is moved backward by the back gear, a driver frequently assumes an unnatural driving posture compared to the case of forward running because the progress direction of the vehicle is backward. Therefore, the accelerator manipulability tends to deteriorate. Particularly, in the case of garaging or backward driving due to vehicle direction change, delicate accelerator manipulation at a relatively low speed is frequently necessary. Therefore, it is necessary to improve the accelerator manipulability for backward driving. Moreover, because accelerator manipulation is delicate under backward driving, if a vehicle speed is unexpectedly increased because a driver slightly extremely steps on an accelerator, the accelerator is resultantly excessively stepped on due to the backward acceleration of the vehicle because of the positional relation between the vehicle and the driver's leg even if the driver does not operate the accelerator. Thus, the vehicle speed may be further increased. Moreover, under backward driving, the driver frequently turns backward and thereby brake manipulation may be delayed. Therefore, if these states occur at the same time, the vehicle may contact a rear object in the worst case under backward driving which is frequently performed in a narrow place.